Material recycling of post-consumer flexible polyethylene packaging waste

Other conference contribution, 2023

The growing concern in society has led to ambitious targets set by EU directives for an increased rate
of recycling on plastic packaging waste, however the challenges involved in material recycling require
better understanding on the development of the performance of the material. The purpose of this
work was to study the properties of post-consumer flexible polyethylene packaging waste, using
material sorted on a large scale from two different sources. Unwashed, laboratory-scale washed,
industrial-scale washed, and industrial-scale washed and melt-compounded (industrially recycled)
materials were used. The unwashed and washed flakes were melt-compounded on a laboratory scale
with a twin-screw extruder using two different temperature profiles and two screw configurations. The
pellets were then injection moulded into a shape of a frame with the purpose to obtain different
material structures: sections with a mixed molecular orientation, a unidirectional flow and a weld line.
The characteristics of the pellets were analysed with GPC, MFR and capillary rheometry. Moreover, the
degradation status, thermal and mechanical properties of the samples were assessed. The washing
reduced the polymer molecular mass and the melt viscosity, making the material susceptible to further
degradation during melt-compounding and more so at a higher temperature. The Young’s modulus
and tensile strength were affected by the washing but not by the compounding temperature or screw
configuration, while the elongation at break were affected somewhat both by the washing and
compounding temperature but not by the screw configuration. The moulded samples made of
unwashed, laboratory-washed and industrial-washed materials had a stiffness, a tensile strength and
an elongation at break as expected of conventional polyethylene grades available. The industrially
recycled samples, however, had a lower stiffness, a slightly higher tensile strength and a significantly
greater elongation at break. This significantly different mechanical properties of the industrially
recycled material were probably due to the degradation at recycling processing, possibly also to the
additives in industrial melt-compounding.